Not applicable.
REFERENCE TO A MICROFICHE APPENDIX, IF ANY
Not applicable.
1. Field of the Invention.
The present invention relates, generally, to detection apparatus and methods. More particularly, the invention relates to detection apparatus and methods that use digitally encoded serial data streams. The invention provides a means to control a variety of equipment, devices or processes based upon an external event that influences a transmission medium into either a Data Pass Through State or a No Data Pass Through State. The verification of the error-free return of the transmitted encoded serial data stream provides proof that, depending on the design of the system, the external event either has or has not occurred. The apparatus and methods of this invention may be used in conjunction with commercial and institutional food service beverage and ice dispensing systems, medical and pharmaceutical dispensing systems, automated manufacturing and production systems, food processing systems, packaging systems, and a variety of other systems.
2. Background Information.
A difficulty with known detection apparatus and methods is distinguishing valid signals from noise. This invention employs digital data error detection principles to verify that a received signal accurately matches a transmitted signal to indicate whether an external event has or has not occurred. Noise rejection or avoidance in sensor systems has usually been attacked using one of two methods. The first method simply looks for xe2x80x9ccleanxe2x80x9d time slots without noise and transmits signals during these clean time slots. The second method transmits a master-clocked continuous pulsed signal and a corresponding master-clocked synchronous signal, and then verifies that the received signal exactly matches both the transmitted pulsed and synchronous signals. This invention differs significantly from known art. No attempt is made to pre-filter the noise to a relatively low level with respect to the signal nor to identify xe2x80x9ccleanxe2x80x9d time slots in which to transmit a signal. Moreover, this method does not depend on a master clock, a continuous pulsed signal, or a corresponding synchronous circuit. Rather, the present invention transmits a serial data stream. Both the data content and the period between serial data stream transmissions may be varied. This asynchronous transmission of digitally-encoded serial data streams provides an effective method for distinguishing valid signals from noise.
The present invention can be used for both proximity based and non-proximity based detection systems. U.S. Pat. No. 5,902,998 and U.S. patent application No. 09/289,902, now U.S. Pat. No. 6,289,902, both assigned to applicants"" assignee Control Products, Inc. and hereby incorporated by reference, disclose the digital data error detection principles of the present invention as part of a proximity detection apparatus for detecting objects within a predetermined region, and more specifically as part of a drink dispenser. A broad category of non-proximity based applications is fluid detection. Any fluid that is at least as conductive as water can be used as a data transmission medium. The present invention can detect fluid level and flow, and can perform other traditional fluid detection functions, and further can detect the presence of a conductive fluid that is the result of a specific step within a complex process. One such application exists in automatic ice making machines, wherein the completion of the ice making cycle is determined by detecting the presence of water in a precise predetermined region.
A common method of making ice includes the step of running or sheeting water over a cold surface. The cold surface may be a grid in which the grid element dimensions determine the width, height, and thickness of ice cubes. The grid is thermally connected to evaporation coils of refrigeration equipment. To produce ice cubes, refrigerant is circulated through the evaporator coils to cool the ice cube grid well below the freezing point of water. Water is delivered through holes in a water trough positioned above the grid. Water runs down over the ice cube grid and flows into the grid cavities due to the Coanda effect. Excess water is collected in a reservoir trough and recirculated back to the water trough. Individual cubes are formed within the grid cavities as the sheets of water freeze. Ice begins to bridge the barriers or grid elements between cavities after the cavities are filled. The refrigeration and water sheeting are stopped when the cubes reach the desired thickness. The cubes usually are harvested into a storage bin by running hot refrigeration gas through the evaporator coils so as to warm the grid enough to release the cubes.
As described in U.S. Pat. No. 5,761,919, known methods for monitoring the thickness of ice cubes include mechanical ice detectors which actuate when the ice builds out enough to touch a microswitch actuator, thermal ice detectors which present a unique thermal signature to the detector when in contact with ice, and electrical resistance ice detectors which forms a semiconducting bridge between a pair of probes when the ice builds out and forces the water into contact with the probes. The ""919 patent further describes that the mechanical ice detector suffers from mechanical problems such as ice sticking to the actuating surfaces, switch hysteresis, and tolerances, that the thermal ice detector suffers from a poor signal to noise ratio, and that the electrical resistance ice detector suffers from lime buildup, electrolysis and electrode corrosion. Electrolysis involves a chemical reaction that occurs when a DC current is passed through the water. The ""919 patent discloses a method for detecting the thickness of the cubes by mounting a metal sense plate in front of the ice cube grid to establish an air gap between the sense plate and ice cube grid. Wires connect the sense plate and the ice cube grid to sensing circuitry. The sense plate, the ice cube grid and the air gap form a capacitor, wherein the sense plate and grid are the electrodes and the air and ice are the dielectric. As the ice increases in thickness, the water sheet is forced outward until it finally contacts the sense plate. The capacitance of the sensor plate changes since the dielectric constant of water differs from that of air. The sensing circuitry detects the predictable change in the capacitance and signals that the cubes have reached the desired thickness. However, the capacitance may be adversely affected by lime buildup on the sense plate.
This invention provides a detection apparatus and method which is believed to constitute an improvement over existing technology.
The present invention provides a detection apparatus and method that uses digitally encoded serial data streams and the principals of digital data transmission, reception, and error detection to detect the occurrence of an external or a physical event that influences a transmission medium between a Data Pass Through State and a No Data Pass Through State. This invention uses a sensor that selectively enables or disables data from passing through from a sensor input to a sensor output, i.e. data loop back, depending on whether the transmission medium is in the Data Pass Through State or the No Data Pass Through State. A serial data stream is received and verified by control circuitry of the apparatus when the sensor enables a data loop back. This detection scheme is highly tolerant of external noise from a variety of sources. Furthermore, by using a suitable microcontroller or microprocessor, the data content of each transmission and the period between each transmission may be varied. The asynchronous serial data transmission used in this scheme nearly eliminates the dedicated hardware and electronics required by other noise filtering schemes. Additionally, the transmitter and receiver may be located at some distance from the microcontroller or microprocessor by incorporating data line drivers.
Any sensor or sensors may be used that can selectively enable a data loop back by accepting a serial data stream and returning it. Data is received at an input of the sensor and passes through to an output of the sensor if the data loop back is enabled. The data loop back is enabled when the transmission medium is in the Data Pass Through State and the data loop back is disabled when the transmission medium is in the No Data Pass Through State. A software program operating within the microcontroller generates transmitted serial data streams and receives received serial data streams from the sensor output. The processor or microcontroller then verifies or compares the received serial data stream to the transmitted serial data stream. If the received serial data stream exactly matches the transmitted serial data stream, the microcontroller determines that the transmission medium is operating in the Data Pass Through State which, depending on the design of the system, indicates whether or not the anticipated external event has occurred. However, if the received serial data stream does not exactly match the transmitted serial data stream, then the transmission medium may be operating in the No Data Pass Through State or the signal received may have been produced by noise.
The digital data error detection principles of the present invention use a method of error checking similar to traditional full-duplex data transmission in which a remote device in communication with a computer echoes any data received from the computer immediately back to the computer. The computer, having received exactly the same data as it transmitted, has a reasonable expectancy that the remote device received error-free data. In this embodiment, the echo is enabled by the data loop back of the sensor when the transmission medium is in the Data Pass Through State. Because the detected signal is a bit-oriented or digital serial data stream rather than a fixed frequency pulse, more rigorous error detection methods may be invoked to further improve the rejection of externally-generated noise. The asynchronous digitally encoded serial data transmission, reception and error checking of the present invention provide increased resistance to periodic noise and inherent resistance to random noise. Furthermore, the present invention does not pre-scan for possible interference. A single low cost microcontroller or microprocessor performs the control functions of the present invention. With respect to fluid detection applications, the present invention eliminates noise problems caused by spurious drops of water or by electrical devices, and minimizes electrolysis and corrosion by using a stream of digital data rather than a steady-state DC current. The electrolysis may further be minimized by alternating the logic levels of the signal associated with the digital data stream.
The features, benefits and objects of this invention will become clear to those skilled in the art by reference to the following description, claims and drawings.